喀斯特常绿与落叶阔叶混交林过去50年来的碳循环模拟

通过对Forest-DNDC模型的植被和土壤参数本地化校准,以气象插值数据为输入,模拟了贵州省普定县高原型喀斯特次生常绿与落叶阔叶混交林1965~2014年的土壤、植被和生态系统碳循环特征。结果表明,与冷模拟和实测值相比,参数本地化校准后的模型能更准确地模拟春、秋、冬3个季节的土壤呼吸动态,而模拟的夏季土壤呼吸偏小;但统计检验指出,参数修订后的Forest-DNDC模型能够较好地模拟喀斯特森林土壤呼吸,降低了模拟误差,可用于喀斯特常绿与落叶阔叶混交林碳动态的模拟。进一步分析发现,1965~2014年喀斯特森林的碳通量除模拟早期的前3~4年急剧增加之外,随后总初级生产力(GPP)保持相对稳定,植物呼吸(Rplant)和生态系统呼吸(R_(ecosystem))随着森林发育而增加,土壤呼吸(R_(soil))减少,植被净初级生产力(NPP)呈迅速减小趋势;净生态系统碳交换量(NEE)亦较迅速下降,在2013年达到最低值-0.17 t C/ha,喀斯特森林由碳汇变为弱碳源。相关分析表明,年均温度和年降水对喀斯特常绿与落叶阔叶混交林的GPP和R_(soil)没有显著影响,但却显著影响NPP、R_(plant)、R_(ecosystem)和NEE。

Modelling Carbon Cycle of Karst Evergreen and Deciduous Broad-leaved Mixed Forest during the Last 50 Years

Carbon cycle of plant, soil, and the whole ecosystem of plateau-type karst evergreen and deciduous broad-leaved mixed forest in Puding, central Guizhou was simulated from 1 965 to 2014 based on the newly parameterized Forest-DNDC model and driven by interpolated daily climate data. Results showed that, compared with default parameter simulation and observations, the re-parameterized model can more accurately simulate soil respiration rates of spring, autumn and winter, but the summer soil respiration rate was under-simulated. However, statistical tests indicated that the modified Forest-DNDC model could generally simulate soil respiration of karst forest. Modelling errors from the default parameter simulation have been reduced. The model can be further used to simulate carbon dynamics of karst evergreen and deciduous broad-leaved mixed forest. Further simulations indicated that carbon fluxes of karst forest increased rapidly in the beginning of 3-4 years. Then with forest grew, the gross primary productivity(GPP) remained relatively stable, plant respiration(R_plant) and ecosystem respiration(R_ecosystem) increased continuously, and soil respiration(R_soil) and net primary productivity(NPP) rapidly decreased. The net ecosystem exchange(NEE) reduced rapidly and achieved its minimum value of -0.17 tC/ha in 2013, implying that karst evergreen and deciduous broad-leaved mixed forest became from a CO₂ sink to a weak CO₂ source. Correlation analyses indicated that the annual mean temperature and annual total precipitation had no statistically significant effects on GPP and R_soil, but had significant effects on NPP, R_plant, R_ecosystem, and NEE.